1 - (IBAction)changeColor
 2 {
 3     //begin a new transaction
 4     [CATransaction begin];
 5     //set the animation duration to 1 second
 6     [CATransaction setAnimationDuration:1.0];
 7     //add the spin animation on completion
 8     [CATransaction setCompletionBlock:^{
 9         //rotate the layer 90 degrees
10         CGAffineTransform transform = self.colorLayer.affineTransform;
11         transform = CGAffineTransformRotate(transform, M_PI_2);
12         self.colorLayer.affineTransform = transform;
13     }];
14     //randomize the layer background color
15     CGFloat red = arc4random() / (CGFloat)INT_MAX;
16     CGFloat green = arc4random() / (CGFloat)INT_MAX;
17     CGFloat blue = arc4random() / (CGFloat)INT_MAX;
18     self.colorLayer.backgroundColor = [UIColor colorWithRed:red green:green blue:blue alpha:1.0].CGColor;
19     //commit the transaction
20     [CATransaction commit];
21 }